The present invention relates generally to electrical relay devices. More particularly, the present invention is a solid state relay for converting a low current input into a high current output and which provides the combined functions of silent switching and visual indication (LED indicators) of circuit status built directly into the relay housing. In this fashion, the relay provides circuit diagnostic capabilities to notify the user of an open or partially open load condition.
The prior art is well documented with examples of electrical current relay devices, such as are typically employed in vehicle electrical systems. In particular, reference is made to prior art electromechanical and standard ISO relays, examples of which typically incorporate large electronic circuits on printed circuit boards which contain mechanical switches and relays.
One example of the prior art is illustrated in U.S. Pat. No. 4,038,584, issued to Tarchalski, and which discloses a protective arrangement for dependent switching circuits including a fusible resistor in a solid state relay comprising two solid state switches connected in parallel with each other and in series with a load and a source of current. Then the first of the two switches is switched on, the second switch also switches on and conducts, supplying sufficient current to the load to thus reduce the voltage across both switches to that of the voltage drop across the second switch. Upon the second switch failing to become turned on when the first switch is turned on, a higher voltage is experienced across the first switch causing excessive circuit flow through the first switch. At this point, a fusible resistor, located in the circuit of the first switch, is opened at such time and in order to prevent first resulting from overheating of the circuit.
U.S. Pat. No. 4,351,014, issued to Schofield, Jr. discloses a solid state self-checking relay including a main switch adapted to be connected in series with a load and voltage source and responsive to relay opening and closing signals. A secondary switch is connected in parallel with the load and is switched a sense opposite that of the main switch by the relay opening and closing signals. If the main switch fails to open, the secondary switch is closed and the load is short circuited by it. Additionally, a fuse in series with the main switch is blown by the current through the secondary switch in order to latch the relay in the open circuit condition. Self-checking circuits are provided to latch the relay in an open circuit condition if there is any circuit failure.
U.S. Pat. No. 4,280,161, issued to Kuhn, teaches an over-voltage protection network system, particularly for use in preventing over-charging of a car battery such as which typically occurs upon failure of the voltage regulator to control current flow through the field of an automotive alternator. A field current of the circuit is conducted through an interruptible network element, for example a fuse or a relay controlled switch. A voltage sensing network, for example a Zener diode, is connected to control current flow through a controlling element, for example a thyrister, which provides either an auxiliary current to bum out the fuse or a control current to the relay coil to interrupt connection to the field if over-voltage has been sensed. Simultaneously, an indicator lamp is energized to indicate malfunction of the voltage regulator.
Finally, U.S. Pat. No. 4,054,934, issued to Riebs, teaches a solid-state inverse overcurrent relay having a long slender wire connected to respond to a current which is proportional to the line current in a power system. An infrared detector or phototransistor is positioned to sense a predetermined color of radiation from the wire and is connected to fire a silicon controlled rectifier which is connected in series with a trip coil for a circuit breaker. The trip coil and silicon controlled rectifier are connected to an independent DC power source. The long slender wire on energization responds to the current which is proportional line current with the same time current characteristic as a fuse. In an alternate embodiment of the invention the relay is connected to the power system through a bridge rectifier which provides the DC current for operating both the heat responsive wire as well as the infrared detector.
The present invention is a solid state relay for converting a low current input into a high current output and which provides the combined functions of silent switching and visual indication of circuit status built directly into the relay housing. The present invention therefore provides circuit diagnostic capabilities to the relay and which notify the user of an open or partially open circuit load condition.
A three dimensional polygonal shaped housing, preferably cubicle shape, encloses a printed circuit board. The circuit board in the preferred variant defines a bottom side portion of the housing. A MOSFET field effect transistor, a pair of female circuit board terminals, and a pair of LED elements are all electrically communicable with a first side of the printed circuit board in enclosed fashion within the housing. Illuminating head portions of the LED elements extend through apertures defined in a top facing side of the housing and are viewable from an exterior location of the housing.
A fuse includes first and second spaced apart and extending blade portions engageable, respectively, with the first and second female terminals and through additional openings defined in the top face of the housing. A plurality of four male circuit board terminals are in electrical communication with a second side of the printed circuit board, corresponding to the bottom facing side of the housing, and extend from further selected exterior locations of the housing.
A first switching condition contained within a single open load detection portion of the circuit, causes the first LED element to illuminate, indicating an open circuit operating condition of the relay. A second switching condition contained within a multiple open load detection portion of the circuit, causes the second LED element to illuminate, indicating a partial or total open circuit load operating condition.